Abnormal state occurrence predicting method, state deciding apparatus, and image forming system

ABSTRACT

In a state deciding apparatus, an information acquiring unit acquires pieces of information of different types related to a state of an image forming apparatus. An index value calculating unit calculates an index value based on the pieces of information acquired. A state change deciding unit decides a change in a subsequent state of the image forming apparatus, based on a temporal change in the index value calculated.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present document incorporates by reference the entire contents ofJapanese priority document, 2003-184929 filed in Japan on Jun. 27, 2003.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to an image forming system such as acopying machine, a printer, or a facsimile, an abnormal state occurrencepredicting method in the image forming apparatus, and a state decidingapparatus that decides a state of the image forming apparatus.

2) Description of the Related Art

In an image forming apparatus of an electronic photographing scheme,maintenance such as repair, and replacing consumable articles like tonerand a photosensitive member needs to be performed. When a failureoccurs, all or some of the functions of the apparatus must be stoppeduntil repair is finished, and a user has to suffer a time loss.Therefore, if an occurrence of an abnormal state such as occurrence of afailure, or the need for replacing a unit or parts is predicted, and ifnecessary maintenance is performed in advance, the down time can reduce.

Japanese Patent Application Laid-Open Publication No. 2001-175328discloses a conventional method of predicting occurrence of an abnormalstate such as the failure, the end of life of a spare part, or the like.This method performs a statistic process, analogism, or the like topieces of information such as sensing information detected by varioussensors arranged in the image forming apparatus.

However, the above method can predict the possibility of occurrence ofan abnormal state, but cannot predict a time for occurrence of theabnormal state. If the time for occurrence of the abnormal state in theimage forming apparatus can be predicted, maintenance can be performedat appropriate time depending on the degree of urgency of maintenance.Therefore, it is desired to predict, not only the possibility ofoccurrence of an abnormal state in the image forming apparatus but alsoa time when the abnormal state might occur.

SUMMARY OF THE INVENTION

It is an object of the invention to at least solve the problems in theconventional technology.

An abnormal state occurrence predicting method according to an aspect ofthe present invention predicts an occurrence of an abnormal state of animage forming apparatus. The method includes acquiring pieces ofinformation of different types related to a state of the image formingapparatus; calculating an index value based on the pieces of informationacquired; and deciding a change in a subsequent state of the imageforming apparatus, based on a temporal change in the index valuecalculated.

A state deciding apparatus according to another aspect of the presentinvention decides a state of an image forming apparatus. The statedeciding apparatus includes an information acquiring unit that acquirespieces of information of different types related to the state of theimage forming apparatus; an index value calculating unit that calculatesan index value based on the pieces of information acquired; and a statechange deciding unit that decides a change in a subsequent state of theimage forming apparatus, based on a temporal change in the index valuecalculated.

An image forming system according to still another aspect of the presentinvention includes an image forming device that forms an image on arecording medium; and a state change deciding device that decides achange in a state of the image forming device. The state change decidingdevice is a state deciding apparatus and includes an informationacquiring unit that acquires pieces of information of different typesrelated to the state of the image forming device; an index valuecalculating unit that calculates an index value based on the pieces ofinformation acquired; and a state change deciding unit that decides achange in a subsequent state of the image forming device, based on atemporal change in the index value calculated.

The other objects, features, and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed description of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a configuration of an abnormal state occurrenceprediction system;

FIG. 2 is a flowchart of the basic operation of the abnormal stateoccurrence prediction system;

FIG. 3 is a flowchart of a procedure for determining a calculationexpression that is used to calculate an index value;

FIG. 4 is a flowchart of a procedure for calculating the index value;

FIG. 5 is a flowchart of a basic operation of an abnormal stateoccurrence prediction system according to a modification;

FIG. 6 illustrates a configuration of a color copying machine;

FIG. 7 is an enlarged view of a main part of a printer unit in the colorcopying machine;

FIG. 8 is a partially enlarged view of a tandem image forming deviceincluded in the printer unit;

FIG. 9 is a perspective view of a resistance-varying element of a thinfilm type;

FIG. 10 is a perspective view of another resistance-varying element;

FIG. 11 is a perspective view of a humidity sensor;

FIG. 12 is a sectional view of a vibration sensor;

FIG. 13 illustrates a circuit configuration of a toner concentrationdetecting unit;

FIG. 14 is an assembly diagram of coils in the toner concentrationdetecting unit;

FIG. 15 illustrates a circuit configuration of a potential measuringsystem that detects a charging potential;

FIG. 16 is a graph of temporal change in an index value D calculated ina first example;

FIG. 17 is a graph of transition (temporal change) of an index value Dcalculated in a second example; and

FIG. 18 is a graph of transition (temporal change) in an index value Dcalculated in a third example.

DETAILED DESCRIPTION

Exemplary embodiments of an abnormal state occurrence predicting method,a state deciding apparatus, and an image forming system according to thepresent invention will be described below with reference to theaccompanying drawings.

FIG. 1 illustrates a basic configuration of an abnormal state occurrenceprediction system. The abnormal state occurrence prediction systemincludes a state decision apparatus that can employ an abnormal stateoccurrence prediction method according to the present invention. A statedecision apparatus 1 includes an information acquisition unit 2, anindex value calculation unit 3, and a decision unit 4. The informationacquisition unit 2 acquires pieces of information of different typesrelated to an image forming operation of the image forming apparatus.The index value calculation unit 3 calculates only an index value basedon the pieces of information acquired by the information acquisitionunit 2. The decision unit 4 decides (or predicts) a subsequent change instate of the image forming apparatus on the basis of a temporal changein the index value calculated by the index value calculation unit 3. Acontrol unit 5 uses the temporal change in the index value calculatedand the decision made by the decision unit 4, to controls devices in animage forming system 6.

The information acquisition unit 2 acquires various pieces ofinformation (described later), and includes various sensors that detectvarious pieces of sensing information, the control unit 5, acommunication interface that is used to transmit/receive data to/from animage data processing unit (not shown), and the like. The informationacquisition unit 2 transmits a request for data acquisition to thevarious sensors, the control unit 5, and,the image data processing unit.The information acquisition unit 2 can receive the various pieces ofsensing information from the various sensors, control parameterinformation from the control unit 5, and input image information fromthe image data processing unit.

The control unit 5 includes a CPU, RAM, ROM, an I/O interface unit, andthe like.

The index value calculation unit 3 and the decision unit 4 may includesingle-purpose LSIs or the like independently of the control unit 5, andmay be constituted by sharing hardware resources such as a CPU thatincludes the control unit 5.

The information acquired by the information acquisition unit 2 and inputto the index value calculation unit 3 includes sensing information (a),control parameter information (b), input image information (c), and thelike.

The sensing information consists of data obtained by various sensorsarranged inside or around the image forming apparatus. The sensinginformation includes dimensions of the units of the apparatus, the speedof a movable member in the apparatus, time (timing), weight, current,potential, vibration, sound, magnetic force, light intensity,temperature, humidity, and the like.

The control parameter information is general information accumulated asa result of control by the apparatus. The control parameter informationincludes an operation history of a user, power consumption, tonerconsumption, history of various image forming condition settings,warning history, and the like.

The input image information is obtained from information about imagedata that is input to the image forming system 6. The input imageinformation includes a number of accumulated color pixels, a ratio of acharacter part, a ratio of a halftone part, a ratio of color characters,a distribution of toner consumption in a main scanning direction, RGBsignals (total amount of toner in units of pixels), an original size, arimmed original, the types (sizes and fonts) of characters, and thelike.

FIG. 2 is a flowchart of the basic operation of the abnormal stateoccurrence prediction system. The pieces of information of the differenttypes related to states of the image forming apparatus are input to thestate decision apparatus 1 of the abnormal state occurrence predictionsystem (step 1-1). The information acquisition unit 2 acquires thepieces of information of the different types whenever required. In theindex value calculation unit 3, only one index value is calculated by acalculation method that is determined on the basis of the informationacquired (step 1-2). The temporal change in the index value calculatedis used to decide an occurrence of an abnormal state in the imageforming apparatus, or is output to a display or an external apparatus(step 1-3).

Before calculating the index value, a calculation method (calculationexpression) must be determined. In the embodiment, multi-dimensionalspaces, in which different coordinate axes are set, are defined for theinput information, and index values are calculated as distances in themulti-dimensional spaces. Therefore, various combinations of theinformation acquired in FIG. 1 are calculated during the normaloperation of the image forming apparatus.

FIG. 3 is a flowchart of a procedure for determining a calculationmethod (calculation expression) used to calculate the index value

n combinations of k pieces of information related to a state of theimage forming apparatus are acquired while the image forming apparatusis operated (step 2-1). The acquisition of the information is describedabove. A concrete example of the information will be described later.

Table 1 given below shows the configuration of the acquired information.Under the first condition (for example, the first day, the firstapparatus, or the like), k data are obtained. These data are defined asy₁₁, y₁₂, . . . , y_(1k). Similarly, data obtained under the nextcondition (the second day, the second apparatus, or the like) aredefined as y₂₁, y₂₂, . . . , y_(2k). Thus, n combinations of data areobtained. TABLE 1 Combination Type of Information Number (1) (2) . . .(k) 1 Y₁₁ Y₁₂ . . . Y_(1k) 2 Y₂₁ Y₂₂ . . . Y_(2k) . . . . . . n Y_(n1)Y_(n2) . . . Y_(nk) Average Y₁ Y₂ . . . Y_(k) Standard Deviation σ₁ σ₂ .. . σ_(k)

Raw data (e.g., y_(ij)) is standardized by an average (y_(j)) and astandard deviation (ó_(j)) (step 2-2). Table 2 shows a result obtainedby standardizing the data shown in Table 1 using the expression (1)Y _(ij)=(y _(ij) −y _(j))/σ_(j)  (1)with the second group optical system. The variable focal length lenschanges a focal length by changing relative distance between therespective group of optical systems and moves the third group opticalsystem on an optical axis for focusing. In the variable focal lengthlens of this type, the first group optical system includes a negativemeniscus lens, a negative meniscus lens, and a positive lens that aresequentially arranged from the object side. An aspherical surface isformed on at least one surface of the two negative meniscus lenses. Thesecond group optical system includes a cemented lens of a positive lensand a negative lens, a positive lens, and a positive lens that aresequentially arranged from the object side. An aspherical surface isformed on a surface on the object side of the positive lens on the mostobject side. The third group optical system includes one positive lensnot including an aspherical surface.

Typically, in the variable focal length lens of the above-mentionedtype, the first group optical system includes a negative meniscus lens,a negative meniscus lens, and a positive lens that are sequentiallyarranged from an object side, the second group optical system includes acemented lens of a positive lens and a negative lens, a positive lens,and a positive lens that are sequentially arranged from the object side,and the third group optical system includes one positive lens. Moreover,aspherical surfaces are formed on at least one surface of the negativemeniscus lens in the first group optical system and a surface on themost object side in the second group optical system. The third groupoptical system includes only a spherical lens.

In this case, the positive lens of the third group optical system isformed in a meniscus shape, which makes it possible to easily correct animage surface.

When it is assumed that a curvature radius of a surface on an objectside of the positive lens of the third group optical system is R1, and acurvature radius of a surface on an image side of the positive lens ofthe third group optical system is R2, particularly satisfactorycorrection is possible under a condition:−0.75<{(R 1−R 2)/(R 1+R 2)}<−0.65  (1)When (R1−R2)/(R1+R2) is less than the lower limit value of thisconditional expression (1), a peripheral image surface topples to a plusside, that is, in a direction distant from the object. When(R1−R2)/(R1+R2) exceeds the upper limit value, the peripheral imagesurface topples to a minus side.

When it is assumed that a distance between the second group opticalsystem and the third group optical system at the wide-angle end is D23w, a focal length of all the systems at the wide-angle end is fw, and afocal length of the third group optical system is f3, it is madepossible to realize reduction in a shortest photographing distance whileminimizing an increase in a total length of the lens and satisfactorilycorrect aberrations under a condition:1.5<{(D 23 w×f 3)/fw ²}<2.5  (2)When (D23 w×f3)/fw² exceeds the upper limit value of this conditionalexpression (2), it becomes difficult to obtain a satisfactory image dueto an increase in a Pelzval's sum and an increase in a negativedistortion aberration. When (D23 w×f3)/fw² is less than the lower limitvalue, a refracting power of the third group optical system becomes toostrong to secure a distance between the second group optical system andthe third group optical system, which makes correction of an aberrationdifficult.

If a photographing lens unit is constituted using the variable focallength lens described above as an optical system, various aberrationscan be corrected satisfactorily. In addition, a wide photographing rangecan be secured with a shortest photographing distance, and a compactphotographing lens unit can be obtained at low cost.

If a camera is constituted using the variable focal length lensdescribed above as a photographing optical system, various aberrationscan be corrected satisfactorily. In addition, a wide photographing rangecan be secured with a shortest photographing distance, and a compactcamera can be obtained at low cost.

Similarly, if a portable information terminal device is constitutedusing the variable focal length lens described above as a photographingoptical system for a camera functional unit, various aberrations can becorrected satisfactorily. In addition, a wide photographing range can besecured with a shortest photographing distance, and a compact portableinformation terminal device can be obtained at low cost.

Next, specific embodiments based on the embodiment modes of the presentinvention will be explained in detail. First and second embodiments tobe described below are first and second embodiment modes and, at thesame time, are also embodiments of a specific structure according to aspecific numerical example of the variable focal length lens accordingto the present invention. A third embodiment is an embodiment mode of acamera or a portable information terminal device according to thepresent invention in which the photographing lens unit according to thepresent invention, which uses the variable focal length lens indicatedin the first and the second embodiments, is adopted in a photographinglens system.

In the first and the second embodiments indicating the variable focallength lens according to the present invention, a structure of thevariable focal length lens and a specific numerical example thereof areindicated.

In each of the first and the second embodiments, an aberration iscorrected sufficiently. It will be apparent from the first and thesecond embodiments that extremely satisfactory focus performance can besecured while attaining sufficient miniaturization by constituting thevariable focal length lens as in the present invention.

In the following explanation related to the first and the secondembodiment modes, signs described below are used.

When height from an optical axis is assumed to be H, an asphericalsurface is defined by the following expression assuming that adisplacement amount in an optical axis direction from a surface vertexis S, a curvature radius is R, and an aspherical coefficient is A_(2i).$\begin{matrix}{S = {\frac{\left( {1/R} \right) \times H^{2}}{1 + \sqrt{1 - {\left( {1/R} \right)^{2} \times H^{2}}}} + {\sum\limits_{i}{A_{si} \times H^{2i}}}}} & (3)\end{matrix}$

FIGS. 1, 2, and 3 are side views of an optical system of a variablefocal length lens according to a first embodiment of the presentinvention at respective single focal length ends, that is, a wide-angleend, an intermediate focal length, and a long focal length end, that is,a telescopic end.

The variable focal length lens shown in FIGS. 1 to 3 includes a firstlens E1, a second lens E2, a third lens E3, a fourth lens E4, a fifthlens E5, a sixth lens E6, a seventh lens E7, an eighth lens E8, a stopFA, and an optical filter OF. In this case, the first lens E1 to thethird lens E3 constitute a first group optical system G1, the fourthlens E4 to the seventh lens E7 constitute a second group optical systemG2, and the eighth lens E8 constitutes a third group optical system G3.The lenses are supported by appropriate common supporting frames or thelike for each of the groups, and each of the groups of the lensesoperate integrally in zooming or the like. FIGS. 1 to 3 also showsurface numbers of respective optical surfaces.

In FIGS. 1 to 3, for example, the first lens E1, the second lens E2, thethird lens E3, the stop FA, the fourth lens E4, the fifth lens E5, thesixth lens E6, the seventh lens E7, the eighth lens E8, and the opticalfilter OF are sequentially arranged in this order from an object sidesuch as a subject. An image is focused behind the optical filter OFhaving various optical filtering functions.

The first lens E1 is a negative meniscus lens formed to be convex on theobject side, the second lens E2 is a negative meniscus lens formed to beconvex on the object side, and the third lens E3 is a positive lensconsisting of a plano-convex lens with a convex surface thereof facedtoward the object side. The first group optical system G1 including thefirst lens E1 to the third lens E3 presents a negative refracting poweras a whole. The fourth lens E4 is a positive lens consisting of abiconvex lens with a more intense convex surface thereof faced towardthe object side. For example, the fourth lens E4 is a hybrid asphericallens in which an aspherical surface is formed by molding a resinmaterial and attaching the resin material to an object side surfaceconsisting of a glass lens of the fourth lens E4. The fifth lens E5 is anegative lens consisting of a biconcave lens with a more intense concavesurface thereof faced toward the image side. The fourth lens E4 and thefifth lens E5 are sequentially closely adhered and stuck to beintegrally cemented to form a (two) cemented lens. The sixth lens E6 isa positive lens consisting of a biconvex lens. The seventh lens E7 is apositive lens consisting of a biconvex lens with a more intense convexsurface thereof faced toward the image side. The second group opticalsystem G2 including the four lenses, the fourth lens E4 to the seventhlens E7, of three groups presents a positive refracting power as awhole. The stop FA arranged on the object side of the second groupoptical system G2 operates with the second group optical system G2. Theeighth lens E8 is a positive meniscus lens formed to be convex on theobject side. The third group optical system G3 including only thiseighth lens E8 presents a positive refracting power.

When a focal length changes from a wide-angle end (short focus end) toan telescopic end (long focus end), the first group optical system G1moves to the object side so as to draw a concave locus, and the secondgroup optical system G2 moves monotonously. Focusing from an infinity toan object at a short distance is performed by moving the third groupoptical system G3 on an optical axis to the object side. The opticalfilter OF consisting of parallel flat boards, which is arranged on themost object side, is a filter such as a crystal low-pass filter or aninfrared cut filter. According to the movement of the respective groupsassociated with the change of the focal length, variable distancesbetween the respective groups change. The intervals (distances) includean interval D12 between a surface on the most image side of the firstgroup optical system G1, that is, a surface on the image side of thethird lens E3 (surface number 6) and a surface on the object side of thestop FA integrated with the second group optical system G2 (surfacenumber 7), an interval D23 between a surface on the most image side ofthe second group optical system G2, that is, a face on the image side ofthe seventh lens E7 (surface number 15) and a surface on the most objectside of the third group optical system G3, that is, a surface on theobject side of the eighth lens E8 (surface number 16), and an intervalD3F between a surface on the most image side of the third group opticalsystem G3, that is, a surface on the image side of the eighth lens E8(surface number 17) and a surface on the object side of the opticalfilter OF (surface number 18).

In this first embodiment, following the change of the focal length fromthe wide-angle side to the telescopic side, a focal length of the entiresystem changes from 4.33 to 12.22 millimeters, an F-number changes from2.69 to 4.53, and a half angle of view changes from 40° to 16°.Characteristics of the respective optical surfaces are as shown in thefollowing table. TABLE 1 Optical characteristics Curvature RefractiveAbbe Surface radius Interval index number  1 33.126 1.00 1.71300 53.94First lens First  2 6.300 1.35 1.00000 group  3 15.009 1.00 1.8061040.74 Second optical  4* 5.101 1.50 1.00000 lens system  5 9.600 2.471.76182 26.60 Third lens  6 0.000 13.54 1.00000  7 0.000 0.80 1.00000Stop  8* 5.828 0.03 1.50703 53.43 (Resin) Second  9 6.146 3.09 1.7234237.99 Fourth group lens optical 10 −37.803 1.90 1.84666 23.78 Fifth lenssystem 11 5.600 0.35 1.00000 12 13.385 2.03 1.48749 70.44 Sixth lens 13−13.385 0.10 1.00000 14 48.080 1.35 1.48749 70.44 Seventh 15 −18.3701.50 1.00000 lens 16 12.227 1.75 1.51680 64.20 Eighth Third 17 77.1782.10 1.00000 lens group optical system 18 0.000 0.48 1.54892 69.13Filter 19 0.000 0.34 1.54892 69.13 20 0.000 0.50 1.50000 64.00 21 0.000

Respective optical surfaces of a fourth surface and an eighth surfaceshaving surface numbers with an asterisk “*” in table 1 are asphericalsurfaces. Parameters of the respective aspherical surfaces in expression(3) are as shown in the following table. TABLE 2 Aspherical surfacecoefficients Surface 4 8 Aspherical surface A₄ −1.07237E−03 −4.94747E−04coefficients A₆ −2.62545E−05 −1.37113E−05 A₈ −1.39674E−08   8.40768E−07A₁₀ −4.22743E−08 −2.81080E−08 A₁₈ −3.64892E−14 0.

The interval D12 between the first group optical system G1 and the stopFA integrated with the second group optical system G2, the interval D23between the second group optical system G2 and the third group opticalsystem G3, and the interval D3F between the third group optical systemG3 and the optical filter OF change as shown in the following table whenthe focal length changes. TABLE 3 Variable interval Wide-angleTelescopic Surface end Intermediate end D 1 2 13.54 5.56 1.20 D 2 3 1.506.30 15.87 D 3 F 3.87 3.67 1.75

The respective numerical values {(R1−R2)/(R1+R2)} related to conditionalexpression (1) and {(R23 w×f3)/fw²} related to conditional expression(2) described above in this first embodiment are as follows.

Numerical values of conditional expressionsExpression (1)=−0.726Expression (2)=2.23

Therefore, both the numerical values related to the respectiveconditional expressions of the present invention described above in thisfirst embodiment are within the ranges of the respective conditionalexpressions.

FIGS. 4 to 6 show aberration curve diagrams of respective aberrations inthe variable focal length lens shown in FIGS. 1 to 3 according to thefirst embodiment. FIG. 4 is an aberration curve diagram at a wide-angleend, FIG. 5 is an aberration curve diagram at an intermediate focallength, and FIG. 6 is an aberration curve diagram at a telescopic end.In the respective aberration curve diagrams, a broken line in aspherical aberration diagram indicates a sine condition, and a solidline and a broken line in an astigmatism diagram indicate a sagittal anda meridional, respectively.

According to the aberration curve diagrams of FIGS. 4 to 6, it is seenthat an aberration is corrected or controlled satisfactorily by thevariable focal length lens of the structure shown in FIGS. 1 to 3according to the first embodiment of the present invention.

In this way, in the variable focal length lens of the three groups ofnegative-positive-positive, a photographing lens, which is capable ofsatisfactorily correcting various aberrations, has a shortestphotographing distance and a wide photographing range, and is compact,can be realized. In addition, since the third group optical system,which conventionally uses an aspherical lens, can be constituted by aspherical lens, there is also an advantage that manufacturing cost canbe held down.

FIGS. 7, 8 and 9 show structures of an optical system of a variablefocal length lens according to the second embodiment (which is also thesecond embodiment mode) of the present invention at respective singlefocal length ends, that is, a wide-angle end, an intermediate focallength, and a long focal length end, that is, a telescopic end.

The variable focal length lens shown in FIGS. 7 to 9 includes the firstlens E1, the second lens E2, the third lens E3, the fourth lens E4, thefifth lens E5, the sixth lens E6, the seventh lens E7, the eighth lensE8, the stop FA, and the optical filter OF. In this case, the first lensE1 to the third lens E3 constitute the first group optical system G1,the fourth lens E4 to the seventh lens E7 constitute the second groupoptical system G2, and the eighth lens E8 constitutes the third groupoptical system G3. The lenses are supported by appropriate commonsupporting frames or the like for each of the groups, and each of thegroups of the lenses operate integrally in zooming or the like. FIGS. 7to 9 also show surface numbers of respective optical surfaces. Note thatthe respective reference numerals for FIGS. 7 to 9 are usedindependently for each embodiment in order to avoid complication ofexplanations due to an increase in the number of digits of the referencenumerals. Thus, in FIGS. 7 to 9, even if components are denoted byreference numerals common to FIGS. 1 to 3, the components do not alwayshave structures common to the first embodiment.

In FIGS. 7 to 9, for example, the first lens E1, the second lens E2, thethird lens E3, the stop FA, the fourth lens E4, the fifth lens E5, thesixth lens E6, the seventh lens E7, the eighth lens E8, and the opticalfilter OF are sequentially arranged in this order from an object sidesuch as a subject. An image is focused behind the optical filter OFhaving various optical filtering functions.

The first lens E1 is a negative meniscus lens formed to be convex on theobject side, the second lens E2 is a negative meniscus lens formed to beconvex on the object side, and the third lens E3 is a positive lensconsisting of a flat convex lens with a convex surface thereof facedtoward the object side. The first group optical system G1 including thefirst lens E1 to the third lens E3 presents a negative refracting poweras a whole. The fourth lens E4 is a positive lens consisting of abiconvex lens with a more intense convex surface thereof faced towardthe object side. In this case, for example, the fourth lens E4 is also ahybrid aspherical lens in which an aspherical surface is formed bymolding a resin material and attaching the resin material to an objectside surface consisting of a glass lens of the fourth lens E4. The fifthlens E5 is a negative lens consisting of a biconcave lens with a moreintense concave surface thereof faced toward the image side. The fourthlens E4 and the fifth lens E5 are sequentially adhered closely and stuckto be integrally cemented to form a (two) cemented lens.

The sixth lens E6 is a positive lens consisting of a biconvex lens. Theseventh lens E7 is a positive lens consisting of a biconvex lens with amore intense convex surface thereof faced toward the image side. Thesecond group optical system G2 including the four lenses, the fourthlens E4 to the seventh lens E7, of three groups presents a positiverefracting power as a whole. The stop FA arranged on the object side ofthe second group optical system G2 operates with the second groupoptical system G2. The eighth lens E8 is a positive meniscus lens formedto be convex on the object side. The third group optical system G3including only this eighth lens E8 presents a positive refracting power.

When a focal length changes from a wide-angle end to a telescopic end,the first group optical system G1 moves to the object side so as to drawa concave locus, and the second group optical system G2 movesmonotonously. Focusing from an infinity to an object at a short distanceis performed by moving the third group optical system G3 on an opticalaxis to the object side. The optical filter OF consisting of parallelflat boards, which is arranged on the most object side, is a filter suchas a crystal low-pass filter or an infrared cut filter. According to themovement of the respective groups associated with the change of thefocal length, variable intervals among the respective groups change. Theintervals include an interval D12 between a surface on the most imageside of the first group optical system G1, that is, a surface on theimage side of the third lens E3 (surface number 6) and a surface on theobject side of the stop FA integrated with the second group opticalsystem G2 (surface number 7), an interval D23 between a surface on themost image side of the second group optical system G2, that is, a faceon the image side of the seventh lens E7 (surface number 15) and asurface on the most object side of the third group optical system G3,that is, a surface on the object side of the eighth lens E8 (surfacenumber 16), and an interval D3F between a surface on the most image sideof the third group optical system G3, that is, a surface on the imageside of the eighth lens E8 (surface number 17) and a surface on theobject side of the optical filter OF (surface number 18).

In this second embodiment, following the change of the focal length fromthe wide-angle side to the telescopic side, a focal length of the entiresystem changes from 4.33 to 12.22 millimeters, an F-number changes from2.64 to 4.46, and a half angle of view changes from 40° to 16°.Characteristics of the respective optical surfaces are as shown in thefollowing table. TABLE 4 Optical characteristics Curvature RefractiveAbbe Surface radius Interval index number  1 48.743 1.00 1.71300 53.94First lens First  2 7.022 0.99 1.00000 group  3 13.235 1.00 1.8061040.74 Second optical  4* 4.906 1.70 1.00000 lens system  5 9.973 2.411.76182 26.60 Third lens  6 0.000 13.83 1.00000  7 0.000 0.80 1.00000Stop  8* 6.052 0.02 1.50703 53.43 (Resin) Second  9 5.692 3.12 1.7234237.99 Fourth group lens optical 10 −29.737 1.93 1.84666 23.78 Fifth lenssystem 11 5.657 0.32 1.00000 12 14.148 1.95 1.48749 70.44 Sixth lens 13−14.148 0.30 1.00000 14 41.652 1.32 1.48749 70.44 Seventh 15 −18.8431.50 1.00000 lens 16 10.509 1.89 1.51680 64.20 Eighth Third 17 58.1822.14 1.00000 lens group optical system 18 0.000 0.48 1.54892 69.13Filter 19 0.000 0.34 1.54892 69.13 20 0.000 0.50 1.50000 64.00 21 0.000

Respective optical surfaces of a fourth surface and an eighth surface-shaving surface numbers with an asterisk “*” in table 4 are asphericalsurfaces. Parameters of the respective aspherical surfaces in expression(3) are as shown in the following table. TABLE 5 Aspherical surfacecoefficients Surface 4 8 Aspherical surface A₄ −1.17507E−03 −4.43095E−04coefficients A₆ −3.05276E−05 −1.70593E−05 A₈   2.02661E−06   1.87848E−06A₁₀ −3.84638E−07 −1.33481E−07 A₁₂   2.31751E−08 0. A₁₄ −8.01568E−10 0.A₁₆   1.52884E−11 0. A₁₈ −2.98849E−13 0.

The interval D12 between the first group optical system G1 and the stopFA integrated with the second group optical system G2, the interval D23between the second group optical system G2 and the third group opticalsystem G3, and the interval D3F between the third group optical systemG3 and the optical filter OF change as shown in the following table whenthe focal length changes. TABLE 6 Variable interval Wide-angleTelescopic Surface end Intermediate end D 1 2 13.83 5.63 1.20 D 2 3 1.506.77 15.81 D 3 F 3.51 3.19 1.79

The respective numerical values {(R1−R2)/(R1+R2)} related to conditionalexpression (1) and {(R23 w×f3)/fw²} related to conditional expression(2) described above in this second embodiment are as follows.

Numerical values of conditional expressionsExpression (1)=−0.694Expression (2)=1.96

Therefore, both the numerical values related to the respectiveconditional expressions of the present invention described above in thissecond embodiment are within the ranges of the respective conditionalexpressions.

FIGS. 10 to 12 show aberration curve diagrams of respective aberrationsin the variable focal length lens shown in FIGS. 7 to 9 according to thesecond embodiment. FIG. 10 is an aberration curve diagram at awide-angle end, FIG. 11 is an aberration curve diagram at anintermediate focal length, and FIG. 12 is an aberration curve diagram ata telescopic end.

According to the aberration curve diagrams of FIGS. 10 to 12, it is seenthat an aberration is also corrected or controlled satisfactorily by thevariable focal length lens of the structure shown in FIGS. 7 to 9according to the second embodiment of the present invention.

A third embodiment of the present invention in which a camera isconstituted by adopting a photographing lens unit, which is constitutedby using the variable focal length lens according to the presentinvention shown in the first and the second embodiments as a zoom lens,as a photographing optical system will be explained with reference toFIG. 13. FIG. 13 is a perspective view showing an appearance of thecamera viewed from a back side thereof which is a photographer side.Note that, although the camera is explained here, a portable informationterminal device such as a so-called PDA (personal data assistant) or acellular phone incorporated with a camera function has been placed onthe market in recent years. Such a portable information terminal deviceincludes substantially the same functions and structure as the camera,although an appearance is slightly different. The variable foal lengthlens according to the present invention may be adopted for such aportable information terminal apparatus.

As shown in FIG. 13, the camera includes a photographing lens unit 101,a shutter button 102, a zoom button 103, an optical finder 104, a liquidcrystal display unit 105, a liquid crystal monitor 106, a main switch107, and the like.

The camera has the photographing lens unit 101 and a light-receivingelement (not shown) serving as an area sensor such as a charge-coupleddevice (CCD) image pickup element. The camera is constituted so as toscan an image of an object to be a photographing target, that is, asubject, which is formed by the photographing lens unit 101 serving as aphotographing optical system, with the light-receiving element. As thisphotographing lens unit 101, the variable focal length lens according tothe present invention as explained in the first and the secondembodiments is used.

An output of the light-receiving element is processed by a signalprocessing device (not shown), which is controlled by a centralprocessing unit (CPU) (not shown), to be converted into digital imageinformation. The image information digitized by the signal processingdevice is subjected to predetermined image processing in an imageprocessing device (not shown), which is also controlled by the centralprocessing unit, and then recorded in a semiconductor memory (not shown)such as a nonvolatile memory. In this case, the semiconductor memory maybe a memory card inserted into a memory card slot or the like or may bea semiconductor memory incorporated in a camera main body. On the liquidcrystal monitor 106, an image being photographed can be displayed as anelectronic finder, and an image recorded in the semiconductor memory canbe displayed. In addition, it is also possible to send the imagerecorded in the semiconductor memory to the outside via a communicationcard or the like inserted into a communication card slot or the like.

The photographing lens unit 101 is in a collapsed state and embedded inthe body of the camera when the camera is carried. When a user operatesthe main switch 107 to turn on a power supply, a barrel is let out asshown in the figure, and the photographing lens unit 101 projects fromthe body of the camera. In this case, in the inside of the barrel of thephotographing lens unit 101, the optical systems of the respectivegroups constituting the variable focal length lens are arranged, forexample, at the short focus end. By operating the zoom button 103, thearrangement of the respective group optical systems is changed, and anoperation for magnification to the long focus end can be performed. Notethat, desirably, the optical finder 104 is also magnified in associationwith a change in an angle of view of the photographing lens unit 101.

In many cases, focusing is performed by a half-press operation of theshutter button 102. In this case, focusing in the variable focal lengthlens including the three groups of negative-positive-positive accordingto the present invention (the variable focal length lens defined inclaims 1 to 5 or indicated in the first and the second embodiments) canbe performed by the movement of the third group optical system G3. Whenthe shutter button 102 is further pressed in and brought into a fullypressed state, photographing is performed, and then the processing asdescribed above is performed.

As described already, the variable focal length lens as indicated in thefirst and the second embodiments can be used as a photographing opticalsystem in the camera or the portable information terminal devicedescribed above. This makes it possible to attain a high-quality andsmall-sized camera or portable information terminal device that uses alight-receiving element with three million to five million pixels orlarger number of pixels. In this case, with the portable informationterminal device, a high-quality image can be photographed and sent tothe outside.

As described above, according to the present invention, a variable focallength lens, which includes a first group optical system having anegative refracting power, a second group optical system having apositive refracting power, and a third group optical system having apositive refracting power sequentially arranged from an object side, hasa stop moving integrally with the second group optical system on theobject side of the second group optical system, and changes a focallength by changing relative intervals of the respective group opticalsystems, can be provided. The variable focal length lens makes itpossible to obtain a wide angle of view and high performance with asmall size and also makes focusing by movement on an optical axis of thethird group optical system possible at low cost. A lens unit, a camera,and a portable information terminal device using the variable focallength lens can also be provided.

In a variable focal length lens according to a first and a secondaspects of the present invention it is possible to satisfactorilyperform the corrections of the various aberrations, secure a widephotographing range with a shortest photographing distance, and realizea compact structure at low cost by reducing the number of asphericalsurfaces.

In a variable focal length lens according to a third aspect of thepresent invention, an image surface can be corrected easily.

A variable focal length lens according to a fourth aspect of the presentinvention is the variable focal length lens according to the thirdaspect. When it is assumed that a curvature radius of a surface on anobject side of the positive lens of the third group optical system isR1, and a curvature radius of a surface on an image side of the positivelens of the third group optical system is R2, the following conditionalexpression is satisfied:−0.75<{(R 1−R 2)/(R 1+R 2)}<−0.65According to the variable focal length lens, in particular, moresatisfactory correction becomes possible.

A variable focal length lens according to a fifth aspect of the presentinvention is the variable focal length lens according to any one of thefirst to the fourth aspects. When it is assumed that a distance betweenthe second group optical system and the third group optical system atthe wide-angle end is D23 w, a focal length of all the systems at thewide-angle end is fw, and a focal length of the third group opticalsystem is f3, the following conditional expression is satisfied:1.5<{(D 23 w×f 3)/fw ²}<2.5According to the variable focal length lens, in particular, it becomespossible to realize reduction in a shortest photographing distance whileminimizing an increase in a total length of the lens and satisfactorilycorrect a distortion aberration and other aberrations.

A photographing lens unit according to a sixth aspect of the presentinvention includes the variable focal length lens according to any oneof the first to the fifth aspects as an optical system. According to thephotographing lens unit, in particular, various aberrations can becorrected satisfactorily, a wide photographing range can be secured witha shortest photographing distance, and it becomes possible to realize acompact structure at low cost.

A camera according to a seventh aspect of the present invention includesthe variable focal length lens according to any one of the first to thefifth aspects as a photographing optical system. According to thecamera, in particular, various aberrations can be correctedsatisfactorily, a wide photographing range can be secured with ashortest photographing distance, and it becomes possible to realize acompact structure at low cost.

A portable information terminal device according to an eighth aspect ofthe present invention includes the variable focal length lens accordingto any one of the first to the fifth aspects as a photographing opticalsystem of a camera function unit. According to the portable informationterminal device, in particular, various aberrations can be correctedsatisfactorily, a wide photographing range can be secured with ashortest photographing distance., and it becomes possible to realize acompact structure at low cost.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

-   To calculate sharpness, an image is obtained by developing or    transferring a line repeat pattern using a single-eye sensor having    a small spot diameter or a line sensor having a high resolution.-   To calculate graininess (feeling of roughness), a halftone image is    read by the same method as the method of detecting sharpness, to    thereby calculate a noise component.-   Resist skew is calculated by the following method. Optical sensors    are arranged at both the ends in the main scanning direction after    resist, and differences between an ON timing of a resist roller and    detection timings of both the sensors are calculated.-   To calculate color resist, a single-eye small-diameter spot sensor    or a high-resolution line sensor detects an edge portion of an    overlapping image on an intermediate transfer body or a sheet of    recording paper.-   Banding (concentration unevenness in a sending direction): a    small-diameter spot sensor or a high-concentration spot sensor    measures the concentration unevenness in a sub-scanning direction on    a sheet of paper, to thereby measure an amount of signal having a    specific frequency.-   A gloss (unevenness) is set by detecting a sheet of recording paper,    on which a uniform image is formed, with a regular reflection    optical sensor.-   Blushing is calculated by the following method. An optical sensor    that detects a relatively large range on a photosensitive body, an    intermediate transfer body, or a sheet of recording paper, reads an    image background portion. Alternatively, a high-resolution area    sensor acquires pieces of image information in respective areas of a    background portion, to thereby count the number of toner particles    included in the image.    (a-8) Physical Characteristic of Print by Image Forming Apparatus-   Stain, blurring, or the like in an image is decided by the following    method. An area sensor detects a toner image on a photosensitive    body, an intermediate transfer body, or a sheet of recording paper,    and the image information acquired is subjected to image processing.-   A gap is calculated by the following method. a high-resolution line    sensor or the area sensor reads an image on the sheet of recording    paper, to thereby calculate an amount of toner dispersed around a    pattern portion.-   A high-resolution line sensor detects void at a rear end and    betakurosu void on the photosensitive body, the intermediate    transfer body, or the sheet of recording paper.-   A displacement sensor detects curling, waving, and bending. Only to    install sensors in positions near both the end portions of the sheet    of recording paper is effective to detect bending.-   To detect rust or scratches in edge surfaces, when delivered sheets    of paper are stocked to some extent, the edge surfaces are    photographed or analyzed by an area sensor vertically arranged on a    paper delivery tray.    (a-9) Environmental State-   For temperature detection, a thermocouple scheme that takes, as a    signal, thermal electromotive force generated at a contact point    between different metals or a metal and a semiconductor joined to    each other, a resistance change, a resistance change element using    that the resistivity of a metal or a semiconductor changes depending    on a temperature, a pyroelectric element in which an arrangement of    charges in a crystal of a certain type is deflected by an increase    in temperature to generate a potential on the surface, a    thermo-magnetic effect element that a change in magnetic    characteristic caused by a temperature, or the like can be employed.-   For detecting humidity, an optical measuring method that measures    optical absorption of H₂O or OH radicals, a humidity sensor that    measures a change in electric resistance of a material caused by    absorption of steam, or the like is used.-   Gases of various types are basically detected by measuring a change    in electric resistance of an oxide semiconductor according to    absorption of the gases.-   In detection of an air-flow (direction, flow rate, and gas type), an    optical measuring method or the like is used. However, when it is    considered that the device is mounted on the system, an air-bridge    flow sensor that can be made more compact is especially useful.-   In detection of air pressure and pressure, a method that measures a    mechanical displacement of a membrane such as a pressure-sensitive    material is used or other methods are used. The method as described    above is used in detection of vibration.

(b) About Control Parameter Information

A control unit determines the operation of the image forming apparatus.Therefore, it is effective to use input/output parameters of the controlunit directly.

(b-1) Image Forming Parameter

The following are examples of direct parameters that are output by anarithmetic process, performed by the control unit, to form an image.

-   Set values of a process condition by the control unit, for example,    a charging potential, a developing bias value, a fixing temperature    set value, and the like-   Similarly, set values of various image processing parameters for    halftone processing, color correction, and the like-   Various parameters set by the control units for the operation of the    apparatus, for example, a timing of paper conveyance, execution time    of a preparation mode before image formation, and the like    (b-2) User Operation History-   Frequency of various operations selected by a user such as the    number of colors, the number of sheets of paper, and image quality    designation-   A frequency of paper side selected by a user    (b-3) Power Consumption-   Total power consumptions in an entire period or in units of specific    periods (one day, one week, one month, or the like) or a    distribution of the total power consumption, a change in power    consumption (derivative), a cumulative value (integral)    (b-4) Consumption of Consumable Articles-   Quantities of toner, photosensitive body, and sheets of paper    consumed in an entire period or in units of specific periods (one    day, one week, one month, or the like) or a distribution of the    consumed quantities, a change in quantity (derivative), and a    cumulative value (integral)    (b-5) Failure Occurrence Information-   Frequency of failure (in units of types) in an entire period or in    units of specific periods (one day, one week, one month, or the    like) or a distribution of the frequencies, a change in frequency    (derivative), and a cumulative value (integral)

(c) Input Image Information

Based on the image information sent from a host computer as direct data,or image information obtained after an original image is read by ascanner and subjected to image processing, the following pieces ofinformation can be acquired.

-   Color pixel cumulative quantity is calculated each time image data    of RGB signals are counted in units of pixels.-   According to a method described in, e.g., Japanese Patent    Publication No. 2621879, an original image is separated into    characters, dots, a photograph, and a background, so that ratios of    a character portion, a halftone portion, and the like can be    calculated. Similarly, a ratio of color characters can also be    calculated.-   Cumulative values of the color pixels are counted in units of    regions partitioned in the main scanning direction, so that a    distribution of toner consumption in the main scanning direction can    be calculated.-   An image size can be calculated by an image size signal generated by    the control unit, or the distribution of color pixels in the image    data.-   Types (size and font) of characters can be calculated from attribute    data of the characters.

The index value D is calculated on the basis of the various pieces ofinformation. A potential probability of occurrence of an abnormal state,such as a failure, is decided on the basis of the index value, tothereby predict occurrence of an abnormal state such as a failure.Basically, as described above, if the index value D is larger than apredetermined threshold value, it is determined that the probability ofoccurrence of a failure is high. The threshold value is generallydetermined by an experiment performed in advance. The initial value ofthe threshold value may be set at an appropriate value (for example,10), and the threshold value may be updated with accumulation of data.

The index value D indicates a measure of a deviation, from a normalstate, of mutual correlation between pieces of information acquired. Ifthe index value is large, deviation from the normal state is determinedas large. Therefore, even though a mechanism of a failure is not known,the probability of occurrence of a failure can be predicted.

After the index value D is calculated, the state of an image formingapparatus is decided on the basis of the index value D to predictoccurrence of an abnormal state. A processing method performedthereafter will be described below. After the index value is calculatedor the occurrence of an abnormal state is predicted, the followingprocesses (d) to (j) can be performed.

(d) Calculation Result, State Decision Result, and Abnormal StateOccurrence Prediction Result are Output

The index value D calculated or a numerical value on which the indexvalue is reflected is output, and a result of predicting an occurrenceof an abnormal state of the image forming apparatus, such as a warningthat lets a user know that a failure is likely to occur, can be output.A temporal change in the index value D, or the numerical value on whichthe index value D is reflected, may be plotted on a graph and output.The following are examples of output methods.

(d-1) Display of Numerical Data or Message on a Display Unit Such asLiquid Crystal Display in an Operation Unit Panel or the Like

(d-2) Announcement and Warning Consisting of Voice or a Sound of aSpecific Pattern Generated by a Sound Output Unit Such as Loudspeaker

(d-3) Recording on Recording Medium (Transfer Paper)

The result of the process (d) is output to a display unit or a soundoutput unit arranged in the corresponding image forming apparatus orrecorded on a recording medium (transfer paper) and output.Additionally, the result may be transferred to a monitoring center thatis connected by a communication network, to monitor the states of thedevices.

(e) Calculation Result, State Decision Result, and Abnormal StateOccurrence Prediction Result are Transferred

The same contents as those in (d) are transferred to a printer server orthe monitoring center.

(f) Calculation Result, State Decision Result, and Abnormal StateOccurrence Prediction Result are Stored

The same contents as those in (d) are stored in storage devices(memories) arranged inside image forming apparatuses, a printer server,and an apparatus of the monitor center. Furthermore, the contents storedin the storage devices are read to make it possible to perform control.

(g) The Apparatus is Stopped

If the index value D calculated exceeds a predetermined reference valueor a rate of increase of the calculated index value D increases, theimage forming apparatus is prevented from being operated in abnormalconditions and maintenance is requested.

(h) Restriction and Control of Operation are Changed

A related portion is estimated on the basis of both the calculationresult of the index value D and information sources. Control changes areperformed such that an operation related to the portion is restricted.The following are examples of the control changes.

(h-1) Change of Color Mode

(h-2) Change of Recording Speed

(h-3) Change of the Number of Halftone Lines

(h-4) Change of Halftone Processing Method

(h-5) Restriction of Paper Type

(h-6) Change in Parameter of Resist Control

(h-7) Change in Parameter of Image Forming Process (for Example, in anImage Forming Apparatus Using an Electronic Photographing Scheme,Charging Potential, an Amount of Exposure, a Developing Bias, a TransferBias, and the Like)

(i) Supply and Exchange of Consumable Article and Component

Supply and exchange are performed automatically by the calculationresult of the index value D.

(j) Automatic Repair

When an abnormal state of a specific portion is found on the basis ofboth the index value D and the information sources, a mode to repair thetarget portion is executed.

Examples that describe a method of acquiring concrete pieces ofinformation in the image forming apparatus according to the embodimentwill be described below. Types of pieces of information used to decidethe state of the image forming apparatus and a method of acquiring thepieces of information are not limited to the following pieces ofinformation and the following method. Pieces of information of varioustypes and features, and other methods of acquiring these pieces ofinformation can be employed.

In a first example, index values or a common index value is calculated,before a product is shipped, using the image forming apparatus shown inFIGS. 6 to 8. After the shipment, the index value is monitored in anon-line manner. Maintenance is performed when the index value increases.Concrete contents of the types of pieces of information to be acquiredand a method of acquiring the pieces of information will be describedbelow.

(1) Temperature

In this example, a unit using a resistance change element that has thesimplest principle and structure, and that can be microminiaturized wasemployed as an information acquiring unit to acquire temperatureinformation.

FIG. 9 is a perspective view of a resistance-varying element of athin-film type used in this example. The resistance change element canbe manufactured as follows. An insulating film 502 is formed on asubstrate 501, and a thin film sensing unit 503 consisting of a metal ora semiconductor material is formed on the insulating film 502.Furthermore, pad electrodes 504 are formed at both the ends of thesensing unit 503, and lead lines 505 are connected. In the resistancechange element, the electric resistance of the sensing unit 503 changeswith a change in surrounding temperature, and hence, the change may bepicked out as a change in voltage or current. Moreover, the sensing unit503 includes a thin film, and therefore, the entire element can be madecompact and can be incorporated in the system.

FIG. 10 is a perspective view of another resistance change element usedin the example. The resistance change element in FIG. 10 is differentfrom that in FIG. 9 in that the sensing unit 503 is arranged on a thinfilm bridge 507 floated from the substrate 501 through spacers 506. Thisstructure prevents heat from being scattered and lost from the sensingunit 503, and the sensing unit 503 has good response to temperature.This structure can detect only radiant heat from a portion to bemeasured, and is preferably used in non-contact measurement.

(2) Humidity

A humidity sensor that can be made compact is useful. The followingbasic principle is used. When humidity-sensitive ceramics adsorbs steam,ion conductivity is increased by adsorbed water to decrease the electricresistance of the ceramics. The material of the humidity-sensitiveceramics may be a porous material consisting of alumina, apatite, orZrO₂—MgO.

FIG. 11 is a perspective view of the humidity sensor used in theembodiment. A comb-shaped electrode 512 is arranged on an insulatingsubstrate 511, and terminals 513 are connected to both the ends of thecomb-shaped electrode 512. In addition, the humidity-sensitive layer 514(generally, humidity-sensitive ceramics) is formed, and the entire areais covered with a case 515. When the humidity-sensitive ceramics adsorbssteam through the case 515, the electric resistance decreases.Therefore, the decrease in electric resistance is measured as a changein voltage or current.

(3) Vibration

1A vibration sensor is basically the same as a sensor that measures airpressure and pressure. When the vibration sensor is mounted on thesystem, a sensor using silicon, which can be microminiaturized, isespecially useful. The motion of a vibrator on a diaphragm consisting ofthin silicon can be measured by measuring a change in capacitancebetween the vibrator and a counter electrode arranged opposite to thevibrator or by using a piezoresistance effect of the Si diaphragmitself.

FIG. 12 is a sectional view of a vibration sensor used in theembodiment. A counter electrode 522 is arranged on an insulatingsubstrate 521. A thin diaphragm 524 and a vibrator 525 are formed on asilicon substrate 523, and a step 526 is formed between the vibrator 525and the counter electrode 522. The resultant structure is joined to theinsulating substrate 521 having the counter electrode 522 manufacturedin advance. The vibrator 525 vibrates according to the vibration orpressure that acts from the surroundings. The vibration may be measuredas a change in capacitance between the vibrator 525 and the counterelectrode 522.

(4) Toner Concentration

A toner concentration for each color is detected. A sensor using aconventionally known scheme can be used as a toner concentration sensor.For example, Japanese Unexamined Patent Publication No. 6-289717discloses a sensing system, for measuring the toner concentration, thatmeasures a change in permeability of the developing agent in adeveloping device.

FIG. 13 illustrates a circuit configuration of a toner concentrationdetecting unit. A reference coil 533 is differentially connected to adetection coil 532 arranged near a developing agent 531 obtained bymixing a magnetic carrier and non-magnetic toner with each other. Theinductance of the detection coil 532 varies with a change inpermeability caused by an increase/decrease in toner concentration(directly, the magnetic carrier). However, the inductance of thereference coil 533 is not influenced by the change in tonerconcentration. An AC drive source 534 that is oscillator driven at afrequency of 500 kHz is connected to the series circuit of the two coils532 and 533 to drive both the coils 532 and 533. A differential outputis picked from the connection point between both the coils 532 and 533.The output is connected to a phase comparator 535, and one of theoutputs from the AC drive source 534 is independently connected to thephase comparator 535, so that the phases of the voltage and thedifferential output voltage from the AC drive source 534 are comparedwith each other.

A sensitivity setting resistor 536 (R1) is connected in parallel to atleast one of the two coils, i.e., the detection coil 532 and thereference coil 533. In FIG. 13, the sensitivity setting resistor 536(R1) is connected to the detection coil 532. The sensitivitycharacteristics are controlled by decreasing the sensitivity to a changein toner concentration. FIG. 14 is an assembly diagram of the coils inthe toner concentration detecting unit. Both the coils 532 and 533 arewound on a cylindrical coil support member 537 such that the coils 532and 533 are vertically adjacent to each other in FIG. 14. The detectioncoil 532 is located on the near side of the developing agent 531 todetect a change in permeability, and the reference coil 533 is locatedon the far side of the developing agent 531 to prevent the permeabilityfrom changing even if the toner concentration changes.

(5) Charging Potential

A charging potential is detected for each color.

FIG. 15 illustrates a circuit configuration of a potential measuringsystem that detects a charging potential used in the example. In FIG.15, a sensor unit substrate 541 is fixed in opposition to an object (notshown). A signal processing unit substrate 542 sends a drive signal tothe sensor unit substrate 541 and receives a sensor output. The sensorunit substrate 541 includes a tuning fork 543 serving as a choppingunit, and a piezoelectric element 544. The piezoelectric element 544 isdriven by a drive signal from the sensor unit substrate 542. In thepotential measuring system, a self-excitation oscillation scheme usingthe following loop is used. When one piezoelectric element 544 isdriven, vibration generated by the piezoelectric element 544 istransmitted to another piezoelectric element 544 a through the tuningfork 543, and the vibration is returned to the drive source. Ameasurement electrode 545 (hereinafter, “an electrode”) receives anelectric flux line from the object. An amplifier 546 amplifies atemporal change of an electric flux line S received by the measurementelectrode 545. The sensor unit substrate 542 includes a piezoelectricelement drive circuit 547, a filter circuit 548, and a phase shiftingcircuit 549. The filter circuit 548 shapes a waveform. The phaseshifting circuit 549 shifts a phase difference between a drive signalmixed in the sensor and an actual drive signal by 180° to cancel thedrive signals. The phase difference between the two signals generallychanges depending on a mixing path. An attenuator 550 controls the sizeof a correction signal, the phase of which is controlled. An addingcircuit 551 adds the correction signal to the sensor output. A signalprocessing circuit 552 processes a final signal output to calculate apotential of an object. Reference numerals 553 and 554 denote controlvolumes of the phase shifting circuit and the attenuator, respectively.

With such configuration, an amount of phase shift and an attenuator gainare controlled to achieve optimization, so that a signal having anopposite phase and an equal level can be added as the correction signalto a mixing signal based on the drive signals, and only a sensor outputbased on a true object can be actually detected. A control unit enablesto correspond to a change in characteristics with aging by a controloperation, and the reliability of the sensor improves.

(6) LD Drive Current

Drive current values of an LD (semiconductor laser) that performs imageexposure are monitored for different colors on a drive circuit, and areused.

(7) Total Counter (the Numbers of Cumulative Print Screens for DifferentColors)

Cumulative data, obtained by counting print screens for differentcolors, is used. For example, when one image is formed in a full colormode, each of the numbers of Y, M C, and Bk print screens is incrementedby one. When one image is formed in a monochromatic (black) mode, onlythe number of Bk print screens is incremented by one. In the Y and Mmodes, the numbers of Y and M print screens are incremented by one each.These data are stored in a storage element, and the result is used.

(8) Developing γ-value

Gradual latent image potentials are formed on a photosensitive body in atest mode, and the latent image is developed under a specific conditionto form a gradual concentration pattern. A reflective concentrationsensor reads the concentration pattern, and a relationship between apotential (potential difference) and the developed reflectiveconcentration is calculated. The inclination of the relationship is setas a γ-value. This value is calculated for each color, and is used.

(9) Developing Start Voltage

Similar to the above configuration, a potential and a developedreflective concentration are calculated in a test mode, and a potentialat which developing is zero is calculated by extrapolation. Thepotential is set as a developing start potential. This value iscalculated for each color and used.

(10) Ratio of Colored Area

From input image information, a ratio of colored area is calculated foreach color on the basis of a ratio of a cumulative value of pixels to becolored and a cumulative value of all the pixels. The ratios of coloredareas are used.

In the example, a test (described below) is performed. A printer testmodel is prepared, and a running test for various pseudo applicationmodes is performed in an experimental laboratory. At this time, data of30 types classified into 10 items are collected several times a day.Some of the collected data are shown in Table 3. TABLE 3 DevelopingDeveloping Toner Charging LD drive γ-value start voltage concentrationpotential current Bk Y M C Bk Y M C Bk Y M C Bk Y M C Bk Y M C 1.39 1.411.63 1.58 −7 −19 −17 −9 3.21 2.75 2.98 2.84 620 600 580 580 656 660 664664 2.06 1.09 1.29 1.26 3 −33 −22 −23 3.31 2.28 2.48 2.58 580 700 640640 664 640 652 652 1.42 1.72 1.79 1.23 −11 −7 1 −20 3.38 2.10 2.47 2.63620 580 580 660 656 664 664 648 1.40 1.49 1.08 1.39 −28 20 31 17 3.502.25 2.68 2.57 600 580 700 620 660 664 640 656 1.08 1.14 1.08 1.18 −11−27 −29 −25 3.34 2.13 2.45 2.40 720 680 700 660 636 644 640 648 1.351.25 1.27 1.25 −17 −31 −26 −25 3.21 2.01 2.37 2.37 640 640 640 640 652652 652 652 1.37 1.48 1.40 1.31 17 18 18 21 3.19 2.27 2.73 2.78 620 600600 640 656 660 660 652 1.05 1.00 1.07 1.17 −18 −30 −39 −33 3.23 2.392.35 2.42 660 740 660 660 648 632 648 648 1.24 1.33 1.48 1.85 −12 −24−20 −6 2.97 2.13 2.37 2.28 660 700 580 620 648 640 684 656 1.41 1.361.27 1.49 −16 −22 −23 −11 3.29 2.08 2.35 2.31 620 620 640 600 656 656652 660 1.37 1.14 1.28 1.41 −27 −29 −23 −14 3.00 2.15 2.47 2.43 600 680640 620 660 644 652 656 1.72 1.34 1.32 1.17 −2 −20 −14 −29 3.69 2.322.61 2.63 580 620 640 680 664 656 652 648 1.49 1.11 1.13 1.19 −13 −25−23 −24 3.46 2.50 2.65 2.61 600 700 680 660 660 640 644 648 : : : : : :: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :Ratio of Environment colored area Vibration Temperature Humidity Bk Y MC Bk Y M C 27.9 40 4.55 6.87 7.73 4.94 4.89 5.65 3.12 4.20 27.0 29 37.41.97 1.58 1.52 4.51 5.03 3.16 4.00 26.6 41 3.73 1.97 1.56 1.54 4.26 4.913.06 3.79 26.6 30 3.72 1.97 1.56 1.57 4.87 4.88 3.29 3.93 26.3 26 3.721.97 1.56 1.58 4.39 5.44 3.06 4.29 26.0 25 3.72 1.98 1.55 1.58 4.61 5.289.65 11.49 26.1 33 3.72 2.02 1.58 1.59 4.94 5.63 7.95 7.08 26.6 24 3.742.04 1.57 1.64 4.36 4.99 7.94 7.09 26.9 27 3.73 2.05 1.57 1.65 4.28 4.967.81 7.37 26.9 30 3.73 2.04 1.56 1.65 4.75 5.06 6.73 7.51 26.6 24 3.732.03 1.55 1.65 4.22 6.37 5.12 7.59 25.3 39 3.72 2.03 1.56 1.65 4.47 5.407.40 7.23 26.6 30 3.71 2.01 1.54 1.64 4.44 5.10 6.88 6.22 : : : : : : :: : : : : : : : : : : : :

Actually, 50 combinations of data were collected. However, meanwhile,the apparatus operated without specific problems. On the basis of thedata, calculations using the numerical expressions (1) to (5) wereperformed to obtain calculation parameters required in the calculationexpression (6). Using the result, the average of the 50 combinations ofvalues D in a normal operation is about 1. In this manner, a calculationmethod (calculation expression) for the index value D was defined.

Products based on the test model were put on sale, and continuouslymonitored in the market. Data to be acquired are the same as that in thetest.

FIG. 16 is a graph of a temporal change in the index value D calculatedin the embodiment. In FIG. 16, an arrow indicates a timing at which aproblem (abnormal state) occurs in the image forming apparatus. Theproblem occurring in this example was toner filming on a photosensitivedrum. Prior to the occurrence of the abnormal state, the index value Dincreases. Based on the result, an increase in the index value D and theoccurrence of an abnormal state strongly correlate with each other. Bytracking the temporal change in the index value D, the occurrence of theproblem (toner filming) is predicted in advance. More specifically,based on the value when the index value D increases, a change of thesubsequent state of the printer is decided. Thus, a period of time takenuntil the index value D becomes a value at which the problem (tonerfilming) occurs can be understood. Therefore, whether the problem (tonerfilming) will occur and also the time at which the problem (tonerfilming) will occur can be predicted.

In the example, the image forming apparatus is connected to a monitoringsystem through a communication network, and the index value D is alwaystransmitted to the monitoring system. The monitoring system monitors achange in the index value D, and is designed to generate a warningsignal when the index value D tends to increase and then exceeds aspecific value. A state in which the warning signal is generated isregarded as a state in which the apparatus has a potential failure, anda service person is dispatched to execute maintenance. The serviceperson directly checks the state of the image forming apparatus,performs necessary processes such as a change of components, andelectrical and mechanical control. After the processes, the serviceperson confirms that the index value D falls within a normal range, andthen ends the maintenance. The index value D or a comment correspondingto the index value D is always displayed to let a user know the state ofthe image forming apparatus. Thus, the user can have a service personattend to the image forming apparatus for advance maintenance.

In a second example, after products are shipped, data are collected inthe market by using 10 printers as field test machines. Measured itemsare the same as those in the first example. One data is collectedeveryday. Data collected for 5 days in a row were employed. Useconditions and environments are different from each other in differentprinters. However, all the printers normally operate during days forwhich the data are collected.

Table 4 contains information acquired in the example. Using these data,calculation parameters of an index value D are determined by the samemethod as in the first example. Thereafter, data of the same items areacquired from a plurality of printers (having the same specifications asthose in the field test machine) except for the field test machines, andindex values D are sequentially calculated. TABLE 4 DevelopingDeveloping Toner Charging Apparatus Data γ-value start voltageconcentration potential number number Bk Y M C Bk Y M C Bk Y M C Bk Y MC 1 1 1.43 1.27 0.94 1.26 −12 −33 −33 −22 3.80 2.96 2.88 2.38 800 640740 640 2 1.43 1.27 0.94 1.26 −12 −33 −33 −22 3.89 2.90 3.13 2.36 600640 740 640 3 1.39 1.15 1.14 1.27 −18 −46 −33 −23 3.56 2.85 2.86 2.26620 660 680 840 . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . 2 1 1.43 1.86 2.13 1.32 −15 −21−1  −27 4.09 3.20 3.30 2.81 600 780 880 840 2 1.31 1.17 1.13 1.08 −8 −25 −27 −32 4.04 2.91 2.84 2.22 640 680 680 700 3 1.41 1.18 1.65 1.51−24 −35 −15 −16 4.08 3.04 2.87 2.25 600 660 580 580 4 1.24 0.98 0.921.05 −15 −47 −38 −41 3.95 2.93 2.82 2.13 640 700 720 660 . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . 3 1 1.36 1.20 0.95 1.01 −28 −42 −44 −40 3.79 3.06 3.21 2.26 600640 720 680 2 1.69 1.07 1.04 1.17 −13 −42 −37 −38 3.89 2.94 3.03 2.32580 700 720 660 3 1.44 0.90 1.04 1.29 −17 −57 −37 −22 4.05 2.88 2.942.43 600 720 720 640 4 1.13 1.29 1.11 0.94 −18 −34 −31 −50 3.99 3.133.30 2.68 620 620 680 700 . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. LD drive Environment Ratio of Apparatus Data current Temper- coloredarea Vibration number number Bk Y M C ature Humidity Bk Y M C Bk Y M C 11 660 652 632 652 24.0 24 3.90 1.98 1.76 1.93 4.88 . . . 2 660 852 832852 24.2 25 3.91 1.98 1.76 1.94 4.54 . . . 3 656 648 644 652 24.8 243.92 1.98 1.77 1.94 4.75 . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . 2 1 660 624 844 652 25.7 26 3.93 2.02 1.811.97 4.29 . . . 2 652 644 644 640 25.5 29 4.00 2.10 1.89 2.04 5.02 . . .3 880 648 664 664 26.1 27 3.99 2.09 1.89 2.04 4.85 . . . 4 652 640 636648 26.4 21 3.99 2.08 1.87 2.03 5.23 . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . 3 1 660 652 636 644 25.9 223.98 2.07 1.88 2.02 4.50 2 664 640 636 648 24.7 24 3.97 2.08 1.85 2.015.30 3 660 636 636 652 25.1 24 3.97 2.07 1.84 2.01 534 4 656 656 648 64026.0 23 3.96 2.06 1.84 2.00 #### . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .

FIG. 17 is a graph of transition (temporal change) of an index value Dcalculated in the second example and related to one specific printer. InFIG. 17, an arrow indicates a timing at which a problem (abnormal state)occurs in an image forming apparatus. In FIG. 17, problem 1 is tonerfilming to a photosensitive body, and problem 2 is rust in the apparatuscaused by toner scattering. In the graph of FIG. 17, the index value Dtends to increase before the problem (abnormal state) actually occurs.In this manner, even though an index value is actually applied to aproduct of the same type that is not the field test machine used indetermination of a calculation method for the index value D, occurrenceof a problem can be predicted by the transition (temporal change) of theindex value, and a countermeasure can be devised.

On the basis of a temporal change when the index value D increases, achange of the subsequent state of the printer is decided, a period oftime taken until the index value D becomes a value at which the problem(toner filming) occurs can be understood. Therefore, whether the problem(toner filming) will occur and the time at which the problem (tonerfilming) will occur can be predicted.

In a third example, after products are shipped, the same items as in thefirst example are acquired for each printer in the market. Data havingthe configuration described in Table 5 was obtained with respect to onespecific printer. Using the data, calculation methods of respectiveindex values D are determined based on the data of the printer thatoperates normally. More specifically, the resultant values are indexvalues D unique to the printer. Thereafter, the index value D iscalculated by the method determined as described above while acquiringthe data of the same items. TABLE 5 Developing Developing Toner ChargingLD drive γ-value start voltage concentration potential current Bk Y M CBk Y M C Bk Y M C Bk Y M C Bk Y M C 1.69 0.93 1.71 1.57  −5  −50 −13 −254.03 3.55 3.39 2.49 580 700 600 600 664 640 660 660 1.38 1.34 1.05 1.07−16 −30 −37 −30 4.08 3.44 3.45 2.38 620 660 700 700 656 648 640 640 1.451.16 0.97 1.27 −19 −47 −45 −29 4.22 3.20 3.26 2.31 600 680 740 640 660644 632 652 1.40 1.07 0.92 1.11 −21 −56 −51 −35 4.51 3.00 3.48 2.38 600680 680 680 660 644 644 644 1.35 0.91 0.93 1.12 −22 −59 −44 −33 4.013.26 3.50 2.45 620 720 680 680 656 636 644 644 2.14 1.91 1.18 1.80  −2 −25 −34 −18 3.96 3.17 3.56 2.38 620 720 660 680 656 636 648 644 1.741.14 1.19 0.68  −9  −40 −26 −65 4.38 3.26 3.63 3.01 580 660 660 800 664648 648 620 1.47 1.01 1.18 0.87 −12 −38 −30 −46 3.86 3.25 3.56 2.69 600700 700 720 660 640 640 636 1.66 1.51 1.13 1.09 −10 −18 −40 −36 3.643.12 3.72 2.41 580 620 680 700 664 656 644 640 1.32 1.28 1.17 1.06 −16−21 −28 −40 3.96 3.01 3.62 2.31 640 640 680 700 652 652 648 640 1.441.15 0.93 1.16 −12 −43 −49 −34 4.17 3.11 3.54 2.46 600 660 700 660 660648 640 648 1.21 1.22 1.04 1.21 −17 −42 −40 −32 3.87 2.88 3.29 2.16 660640 700 680 648 652 640 648 1.33 1.22 0.80 1.05 −19 −36 −80 −36 3.662.73 3.32 2.08 620 640 700 720 656 652 640 636 . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . Ratio of Environment colored area VibrationTemperature Humidity Bk Y M C Bk Y M C 24.7 26 3.94 2.06 1.82 1.97 4.545.95 5.16 6.18 25.2 25 3.95 2.08 1.83 1.98 4.85 5.68 5.40 5.23 25.7 243.94 2.07 1.82 1.97 4.85 4.00 6.87 5.80 24.9 28 3.93 2.07 1.82 1.96 6.115.08 5.36 6.10 25.4 23 3.93 2.07 1.82 1.96 5.02 5.02 6.16 6.25 24.1 313.92 2.07 1,81 1.96 5.53 5.07 5.86 6.67 25.2 26 3.93 2.07 1.81 1.96 5.235.35 5.92 6.95 26.0 25 3.92 2.06 1.80 1.95 4.24 4.92 6.93 6.83 25.5 223.92 2.05 1.80 1.94 4.60 4.09 7.04 6.18 25.8 21 3.92 2.05 1.79 1.94 5.305.31 5.06 6.01 26.2 31 3.91 2.05 1.79 1.94 5.34 4.73 5.45 5.43 28.1 213.90 2.04 1.79 1.94 11.86 4.80 6.21 6.48 25.7 21 3.89 2.03 1.77 1.936.48 4.87 6.62 7.38 . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .

FIG. 18 is a graph of transition (temporal change) in an actual indexvalue D calculated with respect to the printer of the third example. Asin FIG. 18, an arrow indicates a timing at which a problem (abnormalstate), more specifically, toner filming on the photosensitive bodyoccurred. In this case, an index value D, representing failureprediction on which an installation environment and a using state ofeach printer are reflected, is obtained for the printer. Thus, highlyaccurate prediction can be performed. Before a problem (toner filming)actually occurs, the index value D tends to increase. On the basis of atemporal change in the index value D when the index value D increases, achange of the subsequent state of the printer is decided, a period oftime taken until the index value D becomes a value at which the problem(toner filming) occurs can be understood. Thus, whether the problem(toner filming) will occur and the time at which the problem (tonerfilming) will occur can be predicted.

When the index value D indicates a value larger than a predeterminedvalue, the control unit 5 shown in FIG. 1 performs necessary operationcontrol of the image forming system or executes restoration modes.Operations to be controlled include restricting a number of continuousprints, or inhibiting a color output mode. Restoration modes includecleaning a photosensitive body or units around the photosensitive body,control of image concentration or colors (an image or a potential to beformed is detected, and the image or the potential is fed back to biaspower supplies, a motor, or the like to obtain a predetermined value),charging a toner (a developing device is operated to charge the toner),and the like. In addition, an spare parts such as a charging member, acleaning member, and the like arranged in the apparatus may beautomatically replaced.

In a fourth example, the system described in the first example isdesignated to execute an information item deriving mode that calculatesan information item closely correlated to a specifically occurringproblem. More specifically, the information item deriving mode isexecuted as follows.

-   (1) In an initial state (N0), an intermediate state (N1), or a state    immediately before occurrence of a problem (Nt), compare the data of    all the information items of k types with each other.-   (2) Detect whether the state immediately before occurrence of the    problem (Nt) includes an item representing an item extremely    different from the values in the initial state (N0) and the    intermediate state (N1). For example, the absolute value of the    difference between N0 and N1 is compared with the absolute value of    the difference between N0 and Nt. If the latter is five or more    times the former, the item is valid.-   (3) If such an item is present, the item is stored in the storage    device, displayed on the display device, or transmitted to the    monitoring system through a communication network.

Using the data shown in FIG. 17, data on the fifth day was set in theinitial state (N0), data on the fifteenth day was set in theintermediate state (N1), and data on 165th day was set in the stateimmediately before occurrence of the problem (Nt). The numerical valuesin the respective information items are compared with each other. As aresult, the information items having a large difference between thenumerical values are three items described in Table 6. TABLE 6 ProblemInitial Intermediate occurrence state state state Occurring Item (N0)(N1) (Nt) problem Ratio of 2.0 2.2 10.0 Photosensitive colored area bodyfilming Vibration 5 5.5 15.0 Toner 6.5 5 12.0 concentration

These items and the occurring problem are stored in relation to eachother. The stored data are used in system development, so that a highlyaccurate abnormal state occurrence prediction system can be realized. Inthis case, although the initial state and the intermediate state arearbitrarily set, the system must be always operated. A plurality ofintermediate states may be set.

According to the present invention, whether an abnormal state willoccur, and a time at which the abnormal state might occur can bepredicted.

Moreover, occurrence of the abnormal state can be predicted based on atemporal change of a single index value D. Therefore, data processing topredict occurrence of an abnormal state is easy.

Furthermore, the change of the state of the image forming apparatus canbe accurately decided, and hence, an abnormal state can be predictedwith high accuracy.

Moreover, maintenance of the image forming apparatus can be performedbefore the abnormal state actually occurs.

In the embodiment, a calculation method for calculating the index valueD, i.e., a calculation expression for the index value D may bedetermined by the following procedures (1) to (5):

-   (1) Acquire n combinations of pieces of information of k types    selected in advance as the pieces of information of different types    while the image forming apparatus is operated;-   (2) Standardize the (k×n) pieces of information acquired according    to types using averages and standard deviations of the pieces of    information;-   (3) Calculate correlation coefficients of all the combinations of    the (k×n) pieces of information standardized;-   (4) Calculate an inverse matrix of a (k×k) matrix that includes all    correlation coefficients as elements; and-   (5) Define the calculation method (calculation expression), using    all the elements of the inverse matrix.

In this case, the (k×n) pieces of information acquired are standardizedaccording to types using the averages and the standard deviations toreduce influence of the fluctuation of statistical data.

The values of the elements of the inverse matrix used in determining thecalculation method (calculation expression) are large when the valuesare closely related to the state change of the image forming apparatus.Using the elements of the inverse matrix, the index value D can becalculated with a weight, which increases in proportion to therelativity between the state change and the correlation between thepieces of information of the different types. Therefore, the statechange of the image forming apparatus can be decided with higheraccuracy.

With such configuration, occurrence of an abnormal state in the imageforming apparatus can be predicted with higher accuracy.

In the process of determining the calculation method (calculationexpression) described in (1) to (5), the n combinations of pieces ofinformation may be acquired from one image forming apparatus in atime-series manner. Pieces of information used in determining the indexvalue calculation expression can be acquired by using a plurality ofimage forming apparatuses for one test. Thus, developing cost reduces.

Alternatively, the n combinations of pieces of information may beacquired in parallel from the plurality of image forming apparatuses. Inthis case, information acquisition for the determination of thecalculation method (calculation expression) of the index value can beperformed in parallel using the plurality of image forming apparatusesof the same type. Thus, development time reduces.

In the embodiment, different types of abnormal states in the imageforming apparatus may be stored in an information storage unit such thattemporal changes of pieces of information acquired in advance areassociated with the contents of the abnormal states. When the indexvalue D calculated by the index value calculation unit 3 is larger thana predetermined reference value, the contents of an abnormal state,which is expected to occur thereafter, may be specified based on thesubsequent temporal changes of the pieces of information and the piecesof information stored in the image storage unit. In this case, since thecontents of the abnormal state can be specified based on the temporalchange of the pieces of information, prediction accuracy of occurrenceof an abnormal state improves, and more appropriate maintenance can beperformed before occurrence of the abnormal state.

The information storage unit may be a memory such as a RAM constitutingthe control unit 5. An abnormal state contents specifying unit thatspecifies the contents of the abnormal state may be a CPU or the likeconstituting the control unit 5. The information storage unit and theabnormal state contents specifying unit may be constituted by devicesincluding single-purpose LSIs arranged independently of the control unit5. Instead of the contents of the abnormal state, the contents ofmaintenance performed when the abnormal state occurs may be associatedwith the temporal changes of the pieces of information. The contents ofthe abnormal state and the contents of the maintenance performed whenthe abnormal state occurs may be associated with each other.

In this embodiment, a state decision apparatus including a communicationunit may be arranged outside the image forming apparatus. Thecommunication unit may receive the pieces of information used incalculation of the index value D from the image forming apparatusthrough a communication network such as a single-purpose network, apublic network, the Internet, or a local area network. Thus, the imageforming apparatus can be simplified. In addition, a decision of a statechange or prediction of an abnormal state in the image formingapparatuses can be integrally performed by a monitoring center or thelike, in which the state decision apparatus is installed.

In the image forming apparatus according to the embodiment, the controlunit 5 may control the image forming system 6 on the basis of thetemporal change in the index value D. In this case, the image formingsystem 6 can be rapidly controlled such that the state change of theimage forming apparatus is decided to predict occurrence of an abnormalstate. Thus, occurrence of a serious failure can be avoided.

According to the embodiment, the present invention is effectivelyapplied to an image forming apparatus that uses an electronicphotographing scheme including the following processes. A latent imageis formed on an image carrier, the latent image on the image carrier isdeveloped to form a toner image, and the toner image formed istransferred to a recording medium directly or through an intermediatetransfer body. The image forming apparatus of the electronicphotographing scheme has the following characteristic features. (1) Theimage forming apparatus includes a large number of constituent elements,and causal association of the development is complex. (2) The imageforming apparatus is easily affected by ambient operating conditionssuch as temperature or humidity. (3) Consumable parts such as units andcomponents easily deteriorate. (4) Ambient operating conditions largelychange depending on users. Although the complex configuration andphenomenon described above intervenes in the image forming apparatus,occurrence of an abnormal state such as a failure the cause of which isnot clear, can be predicted by simple data processing.

The image forming apparatus according to the embodiment may include anabnormal state prediction result display unit that displays a predictionresult of occurrence of an abnormal state predicted. Thus, a user canknow the occurrence of the abnormal state predicted from the informationdisplayed. Consequently, maintenance can be performed prior tooccurrence of the abnormal state.

The image forming apparatus according to the embodiment may include acommunication unit that transmits a prediction result of occurrence ofan abnormal state predicted to an external device through acommunication network such as a single-purpose network, a publicnetwork, the Internet, or a local area network. In this case, predictionof occurrence of abnormal states in a plurality of image formingapparatuses can be integrally performed by a monitoring center or thelike.

In the image forming apparatus according to the embodiment, the controlunit 5 may control the image forming system 6 on the basis of aprediction result of occurrence of an abnormal state predicted, torestrict an image forming operation. In this case, a specific operationis temporarily restricted, depending on the prediction result, to avoidoccurrence of a serious failure.

In the image forming apparatus according to the embodiment, the controlunit 5 may execute a repair control mode to repair an abnormal state onthe basis of the prediction result. Thus, it is possible to avoidoccurrence of a serious failure.

In the image forming apparatus according to the embodiment, acalculation method for the index value D may be determined each time anoperation of the image forming apparatus is started. Thus, even thoughcorrelation between pieces of information of different types acquiredwith respect to the image forming apparatus and relation between thecorrelation and occurrence of an abnormal state vary, a decision of astate change and prediction of occurrence of an abnormal state can behighly accurate.

According to the present invention, pieces of information of differenttypes related to a state of an image forming apparatus are acquired, andan index value is calculated from the pieces of information acquired.The present inventors examined a relationship between a temporal changein the index value calculated and a state change occurring when theimage forming apparatus is set in an abnormal state, by an experiment orthe like. In this case, the temporal change in the index valuecalculated from the pieces of information corresponds to the statechange of the image forming apparatus. In addition, it was understoodthat, if the index value was different from a value obtained in aninitial normal state by a predetermined amount or more, an abnormalstate such as a failure occurred in the image forming apparatus.Therefore, when the change of the subsequent state of the image formingapparatus is decided on the basis of the temporal change in the indexvalue, a period of time taken until the index value becomes a value atwhich the abnormal state occurs, can be understood. Therefore, whetherthe abnormal state such as a failure will occur, and a time at which theabnormal state might occur can be predicted.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

1. An abnormal state occurrence predicting method that predicts anoccurrence of an abnormal state of an image forming apparatus,comprising: acquiring pieces of information of different types relatedto a state of the image forming apparatus; calculating an index valuebased on the pieces of information acquired; and deciding a change in asubsequent state of the image forming apparatus, based on a temporalchange in the index value calculated.
 2. The abnormal state occurrencepredicting method according to claim 1, wherein the pieces ofinformation of the different types include at least one of a detectionvalue detected by a sensor in the image forming apparatus, a controlparameter used for controlling the image forming apparatus, andinformation related to an input image that is subjected to imageformation.
 3. The abnormal state occurrence predicting method accordingto claim 1, further comprising: determining a calculation method forcalculating the index value, based on the pieces of information acquiredduring a normal operation of the image forming apparatus.
 4. Theabnormal state occurrence predicting method according to claim 3,wherein the determining includes (a) acquiring n combinations of k typesof the pieces of information, selected in advance as the pieces ofinformation of different types, while the image forming apparatus isoperated; (b) standardizing the (k×n) pieces of information acquiredaccording to the types; (c) calculating correlation coefficients of allthe combinations of the (k×n) pieces of information standardized; (d)calculating an inverse matrix of a (k×k) matrix that includes, aselements, all the correlation coefficients calculated; and (e) definingthe calculation method using all the elements of the inverse matrixcalculated.
 5. A state deciding apparatus that decides a state of animage forming apparatus, comprising: an information acquiring unit thatacquires pieces of information of different types related to the stateof the image forming apparatus; an index value calculating unit thatcalculates an index value based on the pieces of information acquired;and a state change deciding unit that decides a change in a subsequentstate of the image forming apparatus, based on a temporal change in theindex value calculated.
 6. The state deciding apparatus according toclaim 5, further comprising: an abnormal state occurrence predictionunit that predicts a time at which an abnormal state occurs in the imageforming apparatus, based on the change in the subsequent state decided.7. The state deciding apparatus according to claim 5, furthercomprising: an index value display unit that displays the temporalchange in the index value.
 8. The state deciding apparatus according toclaim 5, wherein the pieces of information of the different typesinclude at least one of a detection value detected by a sensor in theimage forming apparatus, a control parameter used for controlling theimage forming apparatus, and information related to an input image thatis subjected to image formation.
 9. The state deciding apparatusaccording to claim 5, wherein the index value calculating unitdetermines a calculation method for calculating the index value, basedon the pieces of information acquired during a normal operation of theimage forming apparatus.
 10. The state deciding apparatus according toclaim 9, wherein the index value calculating unit determines thecalculation method by executing the following sequence of steps: (a)acquiring n combinations of k types of the pieces of information,selected in advance as the pieces of information of different types,while the image forming apparatus is operated; (b) standardizing the(k×n) pieces of information acquired according to the types; (c)calculating correlation coefficients of all the combinations of the(k×n) pieces of information standardized; (d) calculating an inversematrix of a (k×k) matrix that includes, as elements, all the correlationcoefficients calculated; and (e) defining the calculation method usingall the elements of the inverse matrix calculated.
 11. The statedeciding apparatus according to claim 10, wherein the informationacquiring unit acquires the n combinations of the pieces of information,in a time-series manner, from one image forming apparatus.
 12. The statedeciding apparatus according to claim 10, wherein the informationacquiring unit acquires the n combinations of the pieces of information,in parallel, from a plurality of image forming apparatuses.
 13. Thestate deciding apparatus according to claim 5, further comprising: aninformation storing unit that stores temporal changes in the pieces ofinformation acquired in advance with respect to different types ofabnormal states of the image forming apparatus, in association withcontents of the abnormal states; and an abnormal state contentspecifying unit that specifies contents of the abnormal state that islikely to occur, if the index value calculated is larger than apredetermined reference value, based on subsequent the temporal changesin the pieces of information and the temporal changes stored.
 14. Thestate deciding apparatus according to claim 5, further comprising: aninformation accepting unit that accepts a plurality of the pieces ofinformation used in calculating the index value, from the image formingapparatus through a communication network.
 15. An image forming systemcomprising: an image forming device that forms an image on a recordingmedium; and a state change deciding device that decides a change in astate of the image forming device, wherein the state change decidingdevice is a state deciding apparatus including an information acquiringunit that acquires pieces of information of different types related tothe state of the image forming device; an index value calculating unitthat calculates an index value based on the pieces of informationacquired; and a state change deciding unit that decides a change in asubsequent state of the image forming device, based on a temporal changein the index value calculated.
 16. The image forming system according toclaim 15, further comprising: a controlling device that controls theimage forming device based on the temporal change in the index value.17. The image forming system according to claim 15, wherein the imageforming device forms a latent image on an image carrier, develops thelatent image to form a toner image, and transfers the toner image to therecording medium in any one way chosen from a group consisting oftransferring directly and transferring through an intermediatetransferring body.
 18. The image forming system according to claim 15,further comprising: an abnormal state prediction display device thatdisplays information about an occurrence of an abnormal state predictedon the basis of the temporal change in the index value.
 19. The imageforming system according to claim 15, further comprising: a predictiontransmitting device that transmits the information about the occurrenceof the abnormal state predicted, to an external device through acommunication network.
 20. The image forming system according to claim16, wherein the controlling device controls the image forming device torestrict an image forming operation based on the change in the state ofthe image forming device decided.
 21. The image forming system accordingto claim 17, wherein the controlling device controls the image formingdevice to restrict an image forming operation based on the change in thestate of the image forming device decided.
 22. The image forming systemaccording to claim 16, wherein the control device executes a repaircontrol mode for repair based on the change in the state of the imageforming device decided.
 23. The image forming system according to claim17, wherein the control device executes a repair control mode for repairbased on the change in the state of the image forming device decided.24. The image forming system according to claim 15, wherein the statechange deciding device determines a calculation method for calculatingthe index value, each time an operation of the image forming device isstarted.